1. Field of the Invention
The present invention is directed generally to a filler layer electrical component having a sintered, monolithic body provided with cavities forming layers, the cavities being filled with metal fillings. The invention is also directed to a method for manufacturing a filler layer electrical component wherein layers are formed into stacks having cavities and the cavities are filled with metal fillings.
2. Description of the Related Art
Electrical multi-layer capacitors having sintered, monolithic ceramic bodies of dielectric material are disclosed in numerous forms in the patent literature. Generally, U.S. Pat. Nos. 3,679,950, 4,071,880, and 4,658,328, the latter of which corresponds to German Published Application No. 36 12 084 are the closest to the present invention of the patent literature.
U.S. Pat. No. 3,697,950 discloses a ceramic multilayer capacitor having a ceramic monolithic body with cavities filled with a metal. The cavities are open in alternation from layer to layer only to the end faces lying opposite one another and are closed to the ajoining lateral faces. Also disclosed in U.S. Pat. No. 3,679,950 is a method for manufacturing an electrical multi-layer capacitor wherein layers are produced from a suspension of material and a suspension is applied on the layers to form limited regions having a defined arrangement so that when the layers are assembled cavitis are formed which are each open only at one side. Since the limited suspension regions which form the cavities in the finished stack of a plurality of layers prepared in this way are closed on practically all sides, it is necessary that the stack be separated into individual ceramic bodies along parting lines, or cutting lines, lying perpendicular relative to one another so that the constituents of the suspension which are volatilized and/or decomposed can be eliminated from the suspension regions so that the cavities are formed in the sintering process.
In addition to other possible materials, metals having low melting points or metal alloys having low melting points are recited for the manufacture of capacitor electrodes within the cavities of the ceramic body. Lead or an alloy of 50% bismuth (Bi), 25% led (Pb) 12.5% 10 (Sn) and 12.5% cadmium (Cd) are examples of a metal and an alloy for such use. The metals and alloys have melting temperatures that are considerably lower than the sintering temperatures of, for example, 1325.degree. C. required for sintering the monolithic ceramic body. Moreover, the alloys when melted hardly moisten the surface of the ceramic bodies at all. The contacts for the capacitor, which are usually composed of silver, are applied to the opposite end faces of the multi-layer capacitor disclosed in U.S. Pat. No. 3,679,950 and are applied after the impression of the molten metal into the ceramic body and after cooling of the saturated ceramic body.
U.S. Pat. No. 4,071,880 discloses practically the same electrical multi-layer capacitor having a sintered monolithic ceramic body as in U.S. Pat. 3,679,950 and the same considerations apply Over and above this, the U.S. Pat. No. 4,071,880 discloses the possibility of applying contacts to the end faces of the monolithic ceramic body before the saturation, or filling, of the cavities of the ceramic body, wherein the contacts are porous. The multi-layer capacitor disclosed therein is composed of a plurality of ceramic layers lying alternately on top of one another and of inner electrodes, as well as outer, double layer electrodes, or contacts, which are connected to the inner electrodes in a predetermined way. For example, a lamella-like electrode structure is present.
During the manufacture of a monolithic multi-layer capacitor of the above reference, untreated or unsintered ceramic laminae, or suspension layers, are first manufactured with the assistance of a stripping of doctor process using a stripper blade. The ceramic laminae so manufactured have a thickness of from 0.05 through 0.1 mm. A coal or carbon paste is then applied or printed onto the surface of the ceramic laminae, the paste being composed of coal or of a ceramic powder and carbon powder. The paste or suspension is applied in limited regions so that the finished ceramic body includes cavities which are open only toward the end faces lying opposite one another in alternation. A plurality of such printed ceramic laminae are arranged lying on top of one another in alternation and are joined to one another by applying a pressure force to form an integrated structure. Individual members are produced from the integrated structure by parting along cut lines which extend perpendicularly relative to one another. The individual members are then fired at a temperature of above 1000.degree. C. to sinter the ceramic laminae and to eliminate the coal or carbon powder within the carbon paste which has been printed thereon. As a result, porous intermediate layers having ceramic powder in regions are produced in which the inner electrodes are to be formed. Following thereupon, the porous outer electrodes are applied to the sintered individual members as contacts. This can be performed, for example, on the basis of methods disclosed in U.S. Pat. Nos. 3,683,849, 4,526,129 and 4,561,954 and in Great British Pat. No. 2,106,714, German Pat. No. 27 22 140 or German Published application No. 36 38 286.
For example, the contacts are obtained by stoving a paste which is principally composed of nickel and which is mixed with a glazing compound. The ceramic body formed in this way is then introduced into a pressure vessel and is then dipped into a molten lead in a decompressed condition which serves as a conductor material for the capacitor coating. The temperature of the molten lead into which the ceramic body is dipped is between about 330.degree. through 360.degree. C. Subsequently, the pressure is raised to about 10 bar (atm) so that the molten lead penetrates, or saturates, under pressure into the cavities in the ceramic body through the porous, outer electrodes. The ceramic body is then removed from the molten lead, is cooled and is again exposed to normal pressure so that inner electrodes of lead are formed. Following thereupon, additional layers which provide for good solderability are applied to the outer electrodes.
To manufacture a multi-layer capacitor as set forth above, the outer electrodes applied to the monolithic ceramic body must be porous and must be formed or manufactured so that entry of the molten lead is initially possible to form the inner electrodes but, on the other hand, so that the lead of the inner electrodes is prevented from flowing out of the cavities of the ceramic body again when the body is removed from the molten lead. The molten metal dare not easily moisten the ceramic body, as expressly recommended in column 10, lines 51-58 of U.S. Pat. No. 4,071,880. In other words, the porous outer electrodes form penetration barriers under certain conditions.
The porous, outer electrodes are mainly composed of nickel which does not react with lead. The adhesion by the outer electrodes o the end faces of the ceramic body depends upon the quantity of glazing compound within the paste of which they are formed, the adhesive strength being improved with an increased amount of the glazing compound in the paste. When greater amounts of glazing compound is added to the paste, however, the number of pores formed in the outer electrodes is diminished so that penetration of lead through the electrodes is more difficult, whereas glass components block the intermediate layers and deteriorate the delivery of lead. The electrostatic capacitance can, therefore, not be set as desired even when the ceramic module is exposed to relatively high temperatures within the melt.
To resolve the described problems, U.S. Pat. No. 4,658,328, which corresponds to German Published Application 36 12 084, proposes that the cavities within the ceramic body be designed so that they are open at both end faces lying opposite one another as well as having a slight opening to the ajoining lateral faces so that the molten metal in the injection process can penetrate not only through the porous contacts, or outer electrodes, but also through the portions of the cavity which are slightly open at the lateral surfaces and are free of the contacts. The molten metal can nonetheless not flow out again from the cavities through the slight openings.
This U.S. patent and corresponding German published application also disclose a method encompassing a manufacturing process wherein contacts which remain porous are applied to the end faces.
German patent applications Nos. 36 27 936 and 36 27 929, which have been filed but have not been published as of the priority date of the present application, disclose multi-layer capacitors having a sintered, monolithic ceramic body and methods for the manufacture thereof. The applications propose that the metal used therein for the capacitor coatings have a low melting point to moisten the surfaces inside the cavities of the ceramic body, in contrast to metals or metal alloys hither to known for these purposes. A series of proposals are made therein for these metals or alloys.
According to these applications, the impression of these metals into the ceramic bodies continues to occur through the openings of the cavities which are directed to only one side, the cavities being either free of a contact at the time of metal impression or being capable of being covered with a porous contact. In the former instance, the contacts are subsequently applied.
The use of a moistening metal has the advantage that the metal no longer flows out of the cavities of the ceramic body when the latter is removed from the metal melt and that bonding of the metal fillings to the contacts is assured. Likewise, detaching of the parts after saturation is thereby facilitated.
The problems that have already been described occur when the metal alloy having a low melting point is impressed through porous contacts into cavities of the ceramic body that are open toward only one side. These problems cannot be eliminated by using metals or metal alloys that moisten well due to the risk of blocking the pores in the porous layer and thus the risk of inadequate filling of the cavities. Given the application of contacts after the impression of the molten metal into the ceramic and after cooling of the filled ceramic bodies, problems can again occur in that the bonding of the inner electrodes inside the ceramic body to the outer electrodes at the end faces can be inadequate.
Ceramic posistors (thermistors having a large positive resistance-temperature characteristic) in a layer format are disclosed, for example, in Great British Patent No. 932,558 and ceramic multi-layer varistors are disclosed, for example, in U.S. Pat. No. 4,675,644 which corresponds to European Published application No. 0 189 087.